[74.10] Evidence for Differential Rotation on a T Tauri Star in NGC 1333

The young cluster NGC 1333 has been photometrically
monitored at Wesleyan University for five years beginning in
October of 2000. A number of periodic variables have been
discovered, among them HBC 338 (Herbig & Bell 1995; VizieR
On-line Catalog: V/73A.) What distinguishes this star from
the hundreds of other periodic variables found by this
program in various young clusters, is that its period has
changed substantially with time. During the first three
years of observation, from October 2000 through March 2003
the star had a significant periodicity at 5.58, 5.57 and
5.52 days, which is a common scatter of periods,
commensurate with the expected error in the period
determination. In other words, the period was stable within
our detection capability. Remarkably, in the 2003/2004
observing season the star was again detected as
significantly periodic, but with a period of 4.47 days. This
dramatic change was confirmed in the 2004/2005 season, when
the star's period was found to be 4.46 days. We reiterate
that no other star in our sample of more than a thousand,
monitored over as much as fifteen years has ever behaved
this way. As Cohen, Herbst & Williams (2004 AJ 127, 1602)
discuss, the typical difference in periods from year-to-year
is 1%, with no example of a clearly significant period
change. There is also no definitive example in the
literature of a T Tauri star changing its period
significantly. This star, appears to be such a case: the
period change is about 20%, which is highly significant. We
discuss the possible causes of this unexpected result and
suggest that it indicates the presence of substantial
differential rotation on the star, in the sense that the
poles rotate more slowly than the equator. Both Alice
Francis and Suarav Dhital were undergraduate summer students
at Wesleyan, supported by the Keck Northeast Astronomy
Consortium. We gratefully acknowledge the support of the NSF
through an REU grant (AST-0353997) that supports the
program.

The author(s) of this abstract have provided an email address
for comments about the abstract:
wherbst@wesleyan.edu